Digital devices have recently been developed, and accordingly have required capacitors to have low impedance and excellent high-frequency characteristics. JP 10-32415A discloses a conventional solid electrolytic capacitor. This capacitor includes an anode body including a porous sintered body made of powder of valve metal, such as tantalum, aluminum, or titanium, foil of the valve metal, and an anode lead made of the valve metal. A dielectric oxide layer is provided on a surface of the anode body by anodizing. A solid electrolytic layer made of conductive polymer, such as polypyrrole, polythiophene, polyaniline, or polyfuran, is formed on the dielectric oxide layer. Then, a cathode layer is formed on the solid electrolytic layer, thus providing a capacitor element. The cathode layer includes a carbon layer made of graphite, and a conductive layer made of silver paste provided on the carbon layer.
The anode lead of the capacitor element is welded to an anode terminal, and the cathode layer is bonded to a cathode terminal with conductive adhesive. The capacitor element is covered with package resin to expose respective portions of the anode terminal and the cathode terminal from a surface of the resin, thus providing the solid electrolytic capacitor. The solid electrolytic layer made of conductive polymer having a small resistance reduces an equivalent series resistance (ESR) of the capacitor.
In this capacitor, the solid electrolyte layer made of conductive polymer does not strongly adhere to the carbon layer, and may allow the carbon layer to be peeled off in high temperatures, thereby increasing a resistance of the interface between the solid electrolyte layer and the carbon layer.
Upon being peeled off from the solid electrolyte layer, the carbon layer allows oxygen to enter from the outside of the capacitor and to have the conductive polymer of the solid electrolyte deteriorate. This may increase a resistance of the conductive polymer, accordingly increasing the ESR of the capacitor.